Liquid-crystal displays, CRT (cathode-ray tube) displays, plasma displays or other displays are required to have high visibility of images displayed on these displays. The reflection of external light from the surface of displays, however, significantly lowers the visibility.
Regarding materials other than displays, for example, building materials of metals or glass, for example, having a gloss surface sometimes cause unprepared light reflection which is obstacle to the way of vehicles and pedestrians.
In order to eliminate the problem of a lowering in visibility of displayed images and the various problems involved, for example, in building materials, caused by the reflection of external light, various antireflection films have been proposed.
A representative example of the proposed antireflection films is an antireflection member described in Japanese Patent Laid-Open No. 80205/1997. This antireflection member comprises a transparent substrate, a hardcoat, and an antireflection optical thin film having a two-layer structure provided in that order. The first layer of the antireflection optical thin film is formed of SnO2, ZnO, In8O3, ITO or the like, and the second layer of the antireflection optical thin film is formed of SiO2, MgF2 or other material having a lower refractive index than the first layer of the antireflection optical thin film. Thus, the claimed advantage of this antireflection member is such that the hardcoat eliminates the susceptibility to scratching, the first layer of the antireflection optical thin film offers antistatic properties, and the first and second layers of the antireflection optical thin film prevent reflection.
In the antireflection member having the above construction, however, a thickness of several tens of nm is necessary for each of the first and second layers of the antireflection optical thin film. An attempt to form these layers, for example, by sputtering requires a lot of time which thus disadvantageously results in low processing speed.
In addition, transparent conductive thin layers formed of ITO or the like posses excellent transparency, but on the other hand, disadvantageously, the corrosion resistance is unsatisfactory.
Further, in the antireflection member having the above construction, the reflectance on red light side and blue light side in the visible light region (wavelength 450 nm to 650 nm), in which humans feels glaring, is not satisfactorily evenly lowered. Specifically, since the antireflection properties vary depending upon the wavelength or incident angle of incident light, a lowering in reflectance in the whole visible light region is not realized and, in this case, a change in color or glare is left.
Further, the antireflection member cannot satisfactorily cope with scratch and stain caused at the time of handling.
For example, for a fine concave-convex film comprising a fine concave-convex portion provided at a pitch of not more than the wavelength of light on the surface of a transparent acrylic resin film or the like, it is known that, at the bottom of concaves and convexes, a major proportion thereof is accounted for by the acrylic resin and, thus, the refractive index of this portion limitlessly becomes close to the light refractive index of the acrylic resin per se (about 1.49), while, toward the surface side of the concaves and convexes, the proportion of the acrylic resin lowers and, instead, the proportion of air increases to provide lower refractive index and, around the outermost surface, the refractive index limitlessly becomes close to the refractive index of air (1.0), whereby the provision of the concaves and convexes has the same effect as a stack of a plurality of layers which have successively varied light refractive indexes.
The use of the fine concave-convex film as an antireflection film, as compared with the conventional construction of a stack of a plurality of layers for constituting an interference layer, has advantages including that a change in color according to the visual angle is less likely to take place, the number of layers constituting the structure is small and, thus, the structure is simple, but on the other hand, this fine concave-convex film is disadvantageous in that, since the surface is formed of very fine concaves and convexes, the film is likely to be scratched.
Further, in the production of the concave-convex film, a method is adopted which comprises providing a visible light-curable or other resin composition (a photoresist), creating cured portions and uncured portions through the utilization of the interference of visible light laser, and performing dissolution development to form fine concaves and convexes. This method requires a lot of time in exposure and development, and, thus, is unsuitable for mass reproduction. Further, a resin composition having a relatively low molecular weight suitable for this process is used as the raw material. Therefore, even in the cured portion, the hardness is not very high, and, thus, the surface hardness is also unsatisfactory.